Low power electrical heating devices are known, being generally required in such environments as fuse boxes, terminal blocks, freezing and clotting point monitors, and the like, in order to inhibit the condensation of moisture in the housings of such equipment. Moisture condensation in essence is the result of the thermal pump effect, i.e. the temperature differences between day and night as well as the temperature differences incident to seasonal changes over the course of the year, on the air confined in the housings. This leads to such defects as increased corrosion, electrical breakdowns in switching equipment, the generation of leakage currents, etc. The principal function of the known low power heating devices thus is to prevent the cooling of the interiors of such housings. This objective is, of course, attained, but nevertheless some disadvantages have been encountered by virtue of the fact that the known heating devices are constructed with the electrical heating resistors open to the atmosphere, i.e. being protected neither against moisture nor against dust. One consequence of this type of construction is that despite high outer surface temperatures, the heat transfer to the surrounding atmosphere is limited. Heating devices characterized by high outer surface temperatures also suffer from another disadvantage, however, in that they cannot be, and in fact are not permitted to be, used in explosion-susceptible environments. When the known low power electric heating devices are incorporated in equipment to protect against the freezing of water-filled pipes or against the dropping of the ambient temperature below the clotting or gelling point of stagnant fluid media, difficulties are also encountered in that the radiation losses are excessive.